Field of the Invention
This invention relates to a resin-packaged semiconductor device and more particularly to improvement in high-power, resin-packaged semiconductor integrated circuits having a plurality of external leads.
2. Description of the Prior Art
In resin-packaged semiconductor integrated circuit (IC) devices, a number of external leads are usually derived in parallel to each other to project from one side surface (single in-line) or from the opposing two side surfaces (dual in-line) of the resin package.
An example of a conventional single in-line resin-packaged, high power, semiconductor IC device is shown in FIGS. 1A to 1C, which is sold under the tradenames of NEC .mu.PC1020H and SANYO A4400 (is similar to one disclosed in Japanese Utility Model Publication No. 51-37420). FIG. 1A shows a perspective view, FIG. 1B a cross-section along the line 1B--1B in FIG. 1A, and FIG. 1C how the semiconductor IC device of FIGS. 1A and 1B is mounted on a chassis and connected to a printed circuit board. In the figures, numeral 1 denotes a resin package, for example of epoxy resin, 2 a plurality of external leads, each having an elongated narrower portion 2a and a wider portion 2b, 3 a heat sink or dissipation fin projecting from the side surface opposite to that from which the leads 2 project, and 4 bolt apertures formed in the heat sink fin for mounting the IC device to a chassis in an electronic instrument or device. Although the interior of the resin package is not shown, an IC pellet is carried at the pellet mounting portion of the heat sink fin. A number of electrodes formed on the surface of the pellet are electrically connected to respective external leads through thin metal wires, e.g., gold wires. The wider portions of the external leads extend to the neighborhood of the pellet carrying portion of the heat sink fin and the gold bonding is made on the ends thereof.
Such IC devices are assembled in electronic devices such as car stereophonic devices together with other discrete electronic components such as transistors, capacitors, resistors, etc. An example of the positional relation of the assembly is shown in FIG. 1C. The elongated portions 2a of the external leads are inserted into the apertures formed in a printed circuit board of the electronic device until the wider portions 2b of the external leads contact with the surface of the printed circuit board and soldered to the leads 43 on the printed circuit board similar to other electronic components 41. On the other hand, the heat sink fin 3 is bent as shown in the figure and attached to a chassis 44 of the electronic device with bolts 45 utilizing the bolt apertures 4.
In the conventional high power, resin-packaged IC device as shown in FIG. 1, however, the length or height h of the heat sink fin 3 is designed as large as possible for increasing the heat dissipation efficiency. Such a high heat sink fin makes the assembly of the IC device in an electronic device required to be compact, such as a car stereophonic device, very difficult. Further, for mounting the IC device firmly on a chassis, the resin package should be held in close contact with the chassis. Here, the heat sink fin should also be in good thermal contact with the chassis while it should be physically firmly fixed to the chassis. For attaining this purpose, the heat sink fin should be bent to bring the main portion located on the same plane as that of the resin surface as shown in FIG. 1C or a portion of the chassis for mounting the heat sink fin should be bent in a similar manner. In either case, an additional manufacturing process is required which raises the manufacturing cost.
Further, in encapsulating a semiconductor pellet in resin according to the conventional method, a pellet is placed at the pellet mounting portion of the heat sink fin and the assembly is molded in resin. Thus, the external leads are located at an off-center position in the thickness direction of the resin package. Thus, there is is no versatility in attaching the IC device to the chassis.
Yet further, since the length in the heat sink fin from the pellet carrying position to the position of contact with the chassis becomes long, there may arise thermal resistivity therebetween and the heat dissipation efficiency cannot be improved sufficiently.